Combined Treatment with Low-Level Laser and rhBMP-2 Promotes Differentiation and Mineralization of Osteoblastic Cells under Hypoxic Stress

Metformin Reduces Bone Resorption in Apical Periodontitis Through Regulation of Osteoblast and Osteoclast Differentiation

INTRODUCTION

We have previously demonstrated that auxiliary metformin therapy promotes healing of apical periodontitis. Here we aimed to investigate the effects of metformin on osteoblast differentiation and osteoclast formation in cultured cells and rat apical periodontitis.

METHODS

Murine pre-osteoblasts MC3T3-E1 and macrophages RAW264.7 were cultured under hypoxia (2% oxygen) or normoxia (21% oxygen) and stimulated with receptor activator of nuclear factor-κB ligand (RANKL) when indicated. Metformin was added to the cultures to evaluate its anti-hypoxic effects. Expressions of osteoblast differentiation regulator runt-related transcription factor 2 (RUNX2), RANKL, and osteoclast marker tartrate-resistant acid phosphatase (TRAP) were assessed by Western blot. Apical periodontitis was induced in mandibular first molars of 10 Sprague-Dawley rats. Root canal therapy with or without metformin supplement was performed. Periapical bone resorption was measured by micro-computed tomography. Immunohistochemistry was used to examine RUNX2, RANKL, and TRAP expressions.

RESULTS

Hypoxia suppressed RUNX2 expression and enhanced RANKL synthesis in pre-osteoblasts. TRAP production increased in macrophages after hypoxia and/or RANKL stimulation. Metformin reversed hypoxia-induced RUNX2 suppression and RANKL synthesis in pre-osteoblasts. Metformin also inhibited hypoxia and RANKL-enhanced TRAP synthesis in macrophages. Intracanal metformin diminished bone loss in rat apical periodontitis. Comparing with vehicle control, cells lining bone surfaces in metformin-treated lesions had significantly stronger expression of RUNX2 and decreased synthesis of RANKL and TRAP.

CONCLUSIONS

Alleviation of bone resorption by intracanal metformin was associated with enhanced osteoblast differentiation and diminished osteoclast formation in rat apical periodontitis. Our results endorsed the role of metformin as an effective medicament for inflammatory bone diseases.

Protein kinase D3 conditional knockout impairs osteoclast formation and increases trabecular bone volume in male mice

Studies using kinase inhibitors have shown that the protein kinase D (PRKD) family of serine/threonine kinases are required for formation and function of osteoclasts in culture. However, the involvement of individual protein kinase D genes and their in vivo significance to skeletal dynamics remains unclear. In the current study we present data indicating that protein kinase D3 is the primary form of PRKD expressed in osteoclasts. We hypothesized that loss of PRKD3 would impair osteoclast formation, thereby decreasing bone resorption and increasing bone mass. Conditional knockout (cKO) of Prkd3 using a murine Cre/Lox system driven by cFms-Cre revealed that its loss in osteoclast-lineage cells reduced osteoclast differentiation and resorptive function in culture. Examination of the Prkd3 cKO mice showed that bone parameters were unaffected in the femur at 4 weeks of age, but consistent with our hypothesis, Prkd3 conditional knockout resulted in 18 % increased trabecular bone mass in male mice at 12 weeks and a similar increase at 6 months. These effects were not observed in female mice. As a further test of our hypothesis, we asked if Prkd3 cKO could protect against bone loss in a ligature-induced periodontal disease model but did not see any reduction in bone destruction in this system. Together, our data indicate that PRKD3 promotes osteoclastogenesis both in vitro and in vivo.

Regulating macrophage-MSC interaction to optimize BMP-2-induced osteogenesis in the local microenvironment

Bone morphogenetic protein (BMP-2) has been approved by the FDA to promote bone regeneration, but uncertain osteogenic effect and dose-dependent side effects may occur. Osteoimmunomodulation plays an important role in growth factor-based osteogenesis. Here, we explored how proinflammatory signals affect the dose-dependent osteogenic potential of BMP-2. We observed that the expression level of local IL-1β did not increase with the dose of BMP-2 in the mouse osteogenesis model. A low dose of BMP-2 could not promote new bone formation, but trigger the release of IL-1β from M1 macrophages. As the dose of BMP-2 increased, the IL-1β expression and M1 infiltration in local microenvironment were inhibited by IL-1Ra from MSCs under osteogenic differentiation induced by BMP-2, and new bone tissues formed, even excessively. Anti-inflammatory drugs (Dexamethasone, Dex) promoted osteogenesis via inhibiting M1 polarization and enhancing BMP-2-induced MSC osteo-differentiation. Thus, we suggest that the osteogenic effect of BMP-2 involves macrophage-MSC interaction that is dependent on BMP-2 dose and based on IL-1R1 ligands, including IL-1β and IL-1Ra. The dose of BMP-2 could be reduced by introducing immunoregulatory strategies.

The Neuropeptide Spexin Promotes the Osteoblast Differentiation of MC3T3-E1 Cells via the MEK/ERK Pathway and Bone Regeneration in a Mouse Calvarial Defect Model

BACKGROUND

The neural regulation of bone regeneration has emerged recently. Spexin (SPX) is a novel neuropeptide and regulates multiple biological functions. However, the effects of SPX on osteogenic differentiation need to be further investigated. Therefore, the aim of this study is to investigate the effects of SPX on osteogenic differentiation, possible underlying mechanisms, and bone regeneration.

METHODS

In this study, MC3T3-E1 cells were treated with various concentrations of SPX. Cell proliferation, osteogenic differentiation marker expressions, alkaline phosphatase (ALP) activity, and mineralization were evaluated using the CCK-8 assay, reverse transcriptase-quantitative polymerase chain reaction (RT-qPCR), ALP staining, and alizarin red S staining, respectively. To determine the underlying molecular mechanism of SPX, the phosphorylation levels of signaling molecules were examined via western blot analysis. Moreover, in vivo bone regeneration by SPX (0.5 and 1 µg/µl) was evaluated in a calvarial defect model. New bone formation was analyzed using micro-computed tomography (micro-CT) and histology.

RESULTS

The results indicated that cell proliferation was not affected by SPX. However, SPX significantly increased ALP activity, mineralization, and the expression of genes for osteogenic differentiation markers, including runt-related transcription factor 2 (Runx2), Alp, collagen alpha-1(I) chain (Col1a1), osteocalcin (Oc), and bone sialoprotein (Bsp). In contrast, SPX downregulated the expression of ectonucleotide pyrophosphatase/phosphodiesterase 1 (Enpp1). Moreover, SPX upregulated phosphorylated mitogen-activated protein kinase kinase (MEK1/2) and extracellular signal-regulated kinase (ERK1/2). In vivo studies, micro-CT and histologic analysis revealed that SPX markedly increased a new bone formation.

CONCLUSION

Overall, these results demonstrated that SPX stimulated osteogenic differentiation in vitro and increased in vivo bone regeneration via the MEK/ERK pathway.

Effectiveness of treating segmental bone defects with a synergistic co-delivery approach with platelet-rich fibrin and tricalcium phosphate

Several studies have applied tricalcium phosphate (TCP) or autografts in bone tissue engineering to enhance the clinical regeneration of bone. Unfortunately, there are several drawbacks related to the use of autografts, including a risk of infection, blood loss, limited quantities, and donor-site morbidities. Platelet-rich fibrin (PRF) is a natural extracellular matrix (ECM) biomaterial that possesses bioactive factors, which can generally be used in regenerative medicine. The goal of the present investigation was to develop osteoconductive TCP incorporated with bioactive PRF for bio-synergistic bone regeneration and examine the potential biological mechanisms and applications. Our in vitro results showed that PRF plus TCP had excellent biosafety and was favorable for initiating osteoblast cell attachment, slow release of bioactive factors, cell proliferation, cell migration, and ECM formation that potentially impacted bone repair. In a rabbit femoral segmental bone defect model, regeneration of bone was considerably augmented in defects locally implanted by PRF plus TCP according to radiographic and histologic examinations. Notably, the outcomes of this investigation suggest that the combination of PRF and TCP possesses novel synergistic and bio-inspired functions that facilitate bone regeneration.

Nano-Hydroxyapatite Scaffold Based on Recombinant Human Bone Morphogenetic Protein 2 and Its Application in Bone Defect Repair

The best way in which to prepare scaffolds with good biological properties is an urgent problem in the field of tissue engineering. In this paper we discuss the preparation of nano-hydroxyapatite scaffold of recombinant human bone morphogenetic protein-2 (rhBMP-2) and its application in bone defect repair. rhBMP-2 reagent was dissolved in 1 mol/L sodium dihydrogen phosphate solution, and the rhBMP-2 solution was added to the nano-hydroxyapatite artificial bone with a 100 μL glass micro dropper at the rate of 10 drops/min to obtain Nano-HA/rhBMP-2 composite artificial bone. In in vivo experiments, rabbits were fixed on an operating table, a 2 cm longitudinal incision was made in the middle part of the radial forearm, and the radius was cut with a wire saw and periosteum, 2.5 cm away from the distal radius. After washing the wound with normal saline, Adv-hBMP-2/MC3T3-E1 nano-HA composite artificial bone, MC3T3-E1 nan-HA composite artificial bone, or Nano-HA artificial bone were implanted in different groups. The artificial bone scaffold prepared in this study has a stronger ability to repair bone defects than the alternatives, and is a promising prospect for the clinical treatment of bone defects.

The impact of photobiomodulation on the chondrogenic potential of adipose-derived stromal/stem cells

Due to their capacity to differentiate into the chondrogenic lineage, adipose-derived stromal/stem cells (ASC) are a promising source of therapeutically relevant cells for cartilage tissue regeneration. Their differentiation potential, however, varies between patients. In our study, we aim to stimulate ASC towards a more reliable chondrogenic phenotype using photobiomodulation (PBM). LED devices of either blue (475 nm), green (516 nm) or red (635 nm) light were used to treat human ASC from donors of varying chondrogenic potential. The treatment was applied either once during the 2D expansion phase or repeatedly during the 3D differentiation phase. Chondrogenic differentiation was assessed via pellet size, GAG/DNA content, histology and gene expression analysis. Reactions to PBM were found to be wavelength-dependent and more pronounced when the treatment was applied during expansion. Donors were assigned to responder categories according to their response to the treatment during expansion, whereby good responders were mainly donors with low intrinsic chondrogenic potential. Exposed to light, they revealed a particularly high relative increase in pellet size (more than twice the size of untreated controls after red light PBM), intense collagen type II immunostaining (low/absent in untreated controls) and activation of otherwise absent COL2A1 expression. Conversely, on a donor with high intrinsic chondrogenic potential, light had adverse effects. When applied with shorter wavelengths (blue, green), it led to reduced pellet size, GAG/DNA content and collagen type II immunostaining. However, when PBM was applied in 3D, the same donor was the only one to react with increased differentiation to all three wavelengths. We were able to demonstrate that PBM can be used to enhance or hamper chondrogenesis of ASC, and that success depends on treatment parameters and intrinsic cellular potential. The improvement of chondrogenesis in donors with low intrinsic potential highlights PBM as potent tool for cell-based cartilage regeneration. Its cost-effectiveness and ease of use make for an attractive treatment option to enhance the performance of ASC in cartilage tissue engineering.

Effect of low power lasers on prokaryotic and eukaryotic cells under different stress condition: a review of the literature

Radiations emitted by low power radiation sources have been applied for therapeutic proposals due to their capacity of inactivating bacteria and cancer cells in photodynamic therapy and stimulating tissue cells in photobiomodulation. Exposure to these radiations could increase cell proliferation in bacterial cultures under stressful conditions. Cells in infected or not infected tissue injuries are also under stressful conditions and photobiomodulation-induced regenerative effect on tissue injuries could be related to effects on stressed cells. The understanding of the effects on cells under stressful conditions could render therapies based on photobiomodulation more efficient as well as expand them. Thus, the objective of this review was to update the studies reporting photobiomodulation on prokaryotic and eukaryotic cells under stress conditions. Exposure to radiations emitted by low power radiation sources could induce adaptive responses enabling cells to survive in stressful conditions, such as those experienced by bacteria in their host and by eukaryotic cells in injured tissues. Adaptive responses could be the basis for clinical photobiomodulation applications, either considering their contraindication for treatment of infected injuries or indication for treatment of injuries, inflammatory process resolution, or tissue regeneration.

Umbilical Cord Mesenchymal Stem Cell-Derived Nanovesicles Potentiate the Bone-Formation Efficacy of Bone Morphogenetic Protein 2

Recombinant human bone morphogenetic protein 2 (rhBMP-2) is one of the most potent osteogenic factors used to treat bone loss. However, at higher doses, rhBMP-2 does not necessarily increase bone formation but rather increases the incidence of adverse side effects. Here, we investigated whether umbilical cord mesenchymal stem cell (UCMSC)-derived nanovesicles (NVs) further increase the in vivo bone formation at high doses of rhBMP-2. In the presence of UCMSC-derived NVs, proliferation, migration, and tube formation of human umbilical vein endothelial cells were stimulated in vitro. Furthermore, migration and osteogenesis of human bone marrow-derived mesenchymal stem cells were stimulated. To examine the efficacy of UCMSC-derived NVs on in vivo bone formation, collagen sponges soaked with rhBMP-2 and UCMSC-derived NVs were used in athymic nude mice with calvarial defects. At a high rhBMP-2 dosage (500 ng/mL), UCMSC-derived NVs significantly promoted bone formation in calvarial defects; however, the UCMSC-derived NVs alone did not induce in vivo bone formation. Our results indicate that UCMSC-derived NVs can potentiate the bone formation efficacy of rhBMP-2 at a high dosage.

Laser and LED photobiomodulation effects in osteogenic or regular medium on rat calvaria osteoblasts obtained by newly forming bone technique

The purposes of this study are to evaluate the effects of photobiomodulation (PBM) with laser and LED on rat calvaria osteoblasts (rGO lineage), cultured in osteogenic (OST) or regular (REG) medium, after induction of a quiescent state and to test if PBM is capable of osteogenic induction and if there is a sum of effects when combining OST medium with PBM. Before irradiation, the cells were put in a quiescent state (1% FBS) 24 h, when red (AlGaInP-660 nm) and infrared laser (GaAlAs-808 nm) and LED (637 ± 15 nm) were applied. The groups were as follows: red laser (RL3-5 J/cm², 3 s and RL5-8.3 J/cm², 5 s, 1.66 W/cm²); infrared laser (IrL3-5 J/cm², 3 s and IrL5-8.3 J/cm², 5 s); LED (LED3-3 s and LED5-5 s, 0.02 J/cm², 0.885 W/cm²); positive (C+, 10% FBS) and negative control (C-, 1% FBS). For alkaline phosphatase (ALP) and mineralization assays, the cells were cultured in REG (DMEM 10% FBS) and OST medium (DMEM 10% FBS, 50 μg/mL ascorbic acid, 10 mM β-glycerophosphate). Statistical analysis was performed using ANOVA and Tukey's tests (p < 0.05). RL5 and LED5 increased proliferation, in vitro wound closure, ALP, and mineralization in rGO cells (p < 0.05). PBM with red laser and LED induced mineralization by itself, without osteogenic medium, not observed for infrared laser (p < 0.05). A sum of effects was observed in osteogenic medium and PBM by infrared, red laser, and LED (5 s). Red laser and LED increased proliferation, migration, and secretory phases in rGO cells in a dose-dependent manner. PBM with red laser and LED promotes osteogenic induction by itself. PBM with infrared laser and osteogenic medium potentializes mineralization.

An injectable cationic hydrogel electrostatically interacted with BMP2 to enhance in vivo osteogenic differentiation of human turbinate mesenchymal stem cells

We have designed and characterized an injectable, electrostatically bonded, in situ-forming hydrogel system consisting of a cationic polyelectrolyte [(methoxy)polyethylene glycol-b-(poly(ε-caprolactone)-ran-poly(L-lactic acid)] (MP) copolymer derivatized with an amine group (MP-NH₂) and anionic BMP2. To the best of our knowledge, there have been hardly any studies that have investigated electrostatically bonded, in situ-forming hydrogel systems consisting of MP-NH₂ and BMP2, with respect to how they promote in vivo osteogenic differentiation of human turbinate mesenchymal stem cells (hTMSCs). Injectable formulations almost immediately formed an electrostatically loaded hydrogel depot containing BMP2, upon injection into mice. The hydrogel features and stability of BMP2 inside the hydrogel were significantly affected by the electrostatic attraction between BMP2 and MP-NH₂. Additionally, the time BMP2 spent inside the hydrogel depot was prolonged in vivo, as evidenced by in vivo near-infrared fluorescence imaging. Biocompatibility was demonstrated by the fact that hTMSCs survived in vivo, even after 8 weeks and even though relatively few macrophages were in the hydrogel depot. The osteogenic capacity of the electrostatically loaded hydrogel implants containing BMP2 was higher than that of a hydrogel that was simply loaded with BMP2, as evidenced by Alizarin Red S, von Kossa, and hematoxylin and eosin staining as well as osteonectin, osteopontin, osteocalcin, and type 1α collagen mRNA expression. The results confirmed that our injectable, in situ-forming hydrogel system, electrostatically loaded with BMP2, can enhance in vivo osteogenic differentiation of hTMSCs.